In a conventional wireless communication network, a large geographic region (such as the United States, for example) is divided into smaller coverage or service areas. A limited number of service providers (e.g., Sprint, Verizon, Cingular, etc.) are authorized to provide wireless services within each service area. Each authorized service provider within a service area, in turn, is allocated a specific frequency band that it may use to provide its wireless services. Hence, the amount of wireless traffic that is possible within a service area is limited by the finite frequency spectrum within that area that has been allocated to the service providers.
Wireless service providers face a number of difficult and intertwined issues. One issue is how to make the most of their finite frequency spectrum within a given service area. This issue has been addressed by division of service areas into smaller sub-areas known as “cells”. FIG. 1 depicts a service area 10 divided into a plurality of cells 12. The basic cell is sometimes referred to as a “macrocell”. Each macrocell 12 has a transmit/receive antenna 14 at its center to provide coverage for users within that cell. By configuring the antenna with an appropriate power and scope of coverage to cover only its cell, frequencies can be re-used in nonadjacent cells, thereby significantly increasing the service provider's traffic handling potential. This concept, which is known as “frequency reuse”, significantly increases the wireless traffic handling capacity within a service area. By dividing its service area into greater numbers of cells, a service provider can increase the traffic handling capacity of the service area and, consequently, its revenue potential for that service area.
An antenna for a macrocell is incorporated along with radio transmission and reception equipment, power sources, controllers, heating/cooling equipment, hook-ups and associated electronics in an installation known in wireless parlance as a “base transceiver station” or simply a “base station”. In a conventional wireless network, the base station is owned by the service provider. Base stations are extremely expensive to constrict, operate and maintain. They are large and complex pieces of equipment, requiring finely-tuned antennae, equipment enclosures, cabling, power sources and backup, weatherproofing and so on. High output power is required to maximize coverage and to penetrate and provide coverage for indoor areas of the cell. They are typically installed on towers, rooftops or street poles that the service provider must have 24 hour access to for maintenance, repairs, upgrades, equipment change-outs and antenna tuning. Many construction, zoning and safety issues are implicated. Hence, a service provider's ability to increase its traffic capacity by dividing its coverage area into more cells is not unbridled; it must be balanced against the increased expenses of constructing, operating and maintaining base stations within those cells.
A conventional wireless network 20 is illustrated in FIG. 2. Network 20 comprises a plurality of base or base transceiver stations (BTSs) 22. Each base station 22 comprises an antenna and associated equipment and is located at the approximate center of a cellular coverage area, as previously described. Base stations 22 establish radio links and communicate with various mobile stations 24 (i.e. mobile telephones or wireless handsets) within their cells. Network 20 also includes a plurality of base station controllers (BSCs) 26, each of which supervises and controls the functioning of multiple base stations 22. Base station controllers 26, in turn are connected to a mobile switching center (MSC) 28. MSC 28 is the hub of network 20. It routes calls from base stations to other base stations or to the PSTN (public switched telephone network) 30 and, conversely, routes calls from PSTN 30 to base stations within its coverage area. Importantly, at least from the standpoint of the service providers, MSC 28 keeps track of the minutes of usage of all mobile stations 24 within its coverage area.
Base stations 22 are connected to BSCs 26 via dedicated lines 25, and BSCs 26 are connected to MSC 28 via dedicated lines 27. MSC 28 is connected to PSTN 30 by a dedicated, high capacity line 29. Lines 25 and 27 may be a high-capacity copper line (T1/T3 lines), a fiber optic cable or a point-to-point microwave relay. Whatever form they take, the costs of laying and/or leasing lines 25 and 27 are quite high and must be borne by the service providers. Thus, in addition to the costs of purchasing or renting the base stations and controllers themselves, the costs of laying and/or leasing dedicated lines between the stations, controllers and switching center must be considered by a service provider that is contemplating adding cells to its service area.
Another issue faced by service providers is the coverage quality and scope it is able to provide within its service area. Call quality and coverage scope are affected by several factors. In congested urban areas, traffic demand often exceeds base station capacity. Division of macrocells into smaller microcells and even smaller picocells, via installation of smaller micro- or pico-base stations at congested, urban hot spots, while less expensive than a full scale base station, still entails the cost of dedicated lines or “backhauls” to connect the equipment to the rest of the network. Conversely, in rural and suburban areas, traffic demand may be significantly lower than capacity and may not justify the costs of a base station and dedicated lines.
In areas where signals are blocked or scattered, such as indoor areas, subways and dense urban areas, signal coverage may be diminished or even non-existent. Providing good coverage in such areas is a major challenge for carriers. A significant indoor penetration loss, ranging from approximately 10-30 dB, must be overcome to achieve coverage inside of a building using an outdoor base station. A network using outdoor base stations that provides good indoor coverage must typically use very high power macro base stations within very small footprints of coverage.